Integrated circuits made from silicon are typically housed in hermetic packages, such as ceramic cavity packages or semi-hermetic plastic packages. However, new integrated circuits utilizing silicon sensors must be exposed to the environment in order to sense the desired variable. For instance, silicon sensors have been developed to sense chemicals in the air, vibrations from sound, radiation from light and color images, as well as temperature and pressure. One application of silicon sensor technology is the sensing of a fingerprint directly from the human hand.
Because silicon sensors must be exposed to the variable being sensed, typical integrated circuit packaging that encases the integrated circuit die in protective enclosures would not be feasible. Instead, the integrated circuit die must be direct mounted in a cavity package or to other substrate in order to expose the sensor to the environment. Because integrated circuits are extremely sensitive, they must be protected from damage caused by exposure to the environment without interfering with the ability to sense the desired variable.
Previous attempts to recognize fingerprint patterns used cumbersome and inefficient techniques. For example, optical sensors, while suitable for their purpose, have the disadvantages of higher power requirements to energize the light source, requiring a larger size to accommodate optical devices, such as lenses, prisms, light emitters, etc., and having a lower reliability, e.g., optical systems can be fooled by photographs. Also, protective coatings over an optical sensor device must be transparent, and reliability is compromised when such coatings become scratched or lose their transparency through exposure to sunlight and the elements. Hence, there is a need for a reliable and durable packaging of exposed silicon sensor dies.